N/A
This invention relates to semiconductor fabrication wafer handling apparatus, and specifically to an automated door assembly to provide controlled access to a substantially contaminant free treatment environment for wafers disposed therein.
Wafer fabrication operations for producing silicon wafers suitable for use with microprocessors, computer memory, and other microcircuits must be carried out in a substantially contaminant-free environment. Airborne particles such as dust and dirt can compromise the quality of the resulting wafer. Excessive foreign matter results in a lower yield of usable wafers from a particular batch. Increasingly dense arrangement of circuit elements on a wafer, or chip, further heightens the quality required to produce a usable wafer. Accordingly, such fabrication operations are often performed in a sealed, substantially contaminant-free processing environment.
Transport of these wafers to and from such a processing environment requires access through an opening in a wall to a sealed chamber in which wafer processing occurs. This processing environment, referred to as the tool side of the wall, contains tools and apparatus for effecting such processing. On the side opposite the processing environment, referred to as the operator side of the wall, transport of the wafers between processing stations occurs by human or robotic operators.
The opening in the wall must be capable of being sealed sufficiently by a door assembly to maintain the contaminant-free state on the tool side, but also be readily unsealed to provide expedient and unobstructed access between the operator and tool sides when needed. Such a seal between the door assembly and the opening often involves close tolerances between moving parts, which raises issues of friction and inaccurate sealing, as wear-and-tear affects the seal mechanism.
The wafers are often stored in a sealed cassette called a pod when they are not in the processing environment on the tool side. Such pods are designed to engage and seal against the opening in the wall from the operator side to allow the wafers to be accessed by a mechanism from the tool side while maintaining the separation between the processing environment and the operator side environment. This separation is achieved by abutting the pod in sealing engagement with the operator side of the wall adjacent the opening therein. Then, the pod door is engaged by the door assembly, unlocked from the pod, and drawn by the door assembly into the tool side. In this manner, the outer perimeter of the pod opening remains sealably engaged with the outer perimeter of the opening in the wall. With the pod door engaged by the door assembly and retracted from the pod, the wafers inside the pod are accessible for processing by apparatus on the tool side. After processing, the wafers are returned to the pod and the door assembly is moved to reengage the pod door with the pod, thereby also closing the opening in the wall with the door assembly. Further, the pod must remain undisturbed when the pod door is open to the processing environment, as manipulation of the pod, such as accidental removal, could disturb the seal and cause physical damage to the wafers.
Automation of such a wafer handling and treatment operation is therefore burdened by the need to manipulate the door assembly and pod door within these close tolerances, the need to accurately re-engage with and reseal the pod door and wall opening following wafer treatment, and the need to secure the pod during treatment to avoid accidental removal. Movement of a door assembly concealing such an opening, however, is typically along two orthogonal axes. Alternatively, a pivoting mechanism is used to effect movement along a single arcuate path.
The present application relates to an automated door assembly and pod latching apparatus for selectively engaging and sealing an opening in a wall which provides access to a substantially contaminant-free environment for wafer processing.
The automated door assembly comprises a base pivotably mounted to a fixed support surface in the sealed environment, and a closure plate linearly movably coupled to the base. The closure plate is configured to seal the opening in the barrier. A closure mechanism is provided comprising a pivoting drive assembly coupled to the base and operable to pivot the base toward and away from the opening along an arcuate path. The closure mechanism also comprises a linear horizontal drive assembly coupled to the closure plate and operable in synchronization with the pivoting drive assembly to force the closure plate to follow a horizontal linear path along an upper portion of the arcuate path of the base adjacent and into contact with the barrier to close the opening. The door assembly also comprises an extendable and retractable arm coupled to the base. The closure plate is disposed on an upper end of the extendable and retractable arm.
When the door assembly is in a fully open position and is not sealed against the opening, the arm is in a retracted position pivoted slightly away from the barrier. As the arm is extended, the closure plate approaches the opening until it reaches a point substantially in front of and obscuring the opening. At this point, the base then pivots inward so that the closure plate approaches the opening on an arcuate path. As the closure plate approaches a position closer to the opening, the linear horizontal drive assembly linearizes the movement of the closure plate. In this manner, the closure plate is directly aligned on a linear path perpendicular to the opening rather than oriented on an arcuate docking path. This engagement provides accurate, effective sealing of the portal door with little force required to overcome friction between the closure plate and the edge of the opening which would otherwise be encountered when moving the closure plate on an arcuate path within close tolerances.
In another embodiment of the invention, a container latching apparatus is provided for latching a container such as a wafer pod or cassette in sealing engagement with the opening on the operator side of the barrier. The container latching apparatus comprises a container or pod support disposed proximate to the opening in the barrier. A platform is linearly movably coupled to the container support. A drive mechanism is coupled to the container support and the platform and is operative to linearly drive the platform with respect to the container support toward and away from the opening in the barrier. A locking mechanism, configured to mate with a corresponding mechanism on the container or pod, is rotatably mounted to the container or pod support and coupled to the platform for linear motion therewith. The platform has mounting pins having beveled upper edges or V-shaped tops for engaging with beveled slots or openings on the underside of the pod to restrict lateral movement of the pod.
After the pod is placed on the platform, the platform is disposed towards the opening and the locking mechanism is rotationally engaged with the corresponding pod locking mechanism to lock the pod. Once engaged with the opening, the closure plate of the door assembly latches onto the pod door, in a manner known in the art, and both are opened enabling the wafers to be processed by various apparatus within the processing environment or tool side. During this time, the pod is secured to the platform by the container latching apparatus, thereby preventing premature removal of the pod, which could lead to wafer damage or contamination of the contaminant-free environment.
In another aspect of the present invention, vertical movement of the closure plate is effected independent of the pivoting movement through the use of a high-resolution servo motor combined with a high-ratio gearbox to drive the extendable portion of the arm via a drive belt. Further, the high-resolution motor works in conjunction with a sensor, such as a optical scanner, provided on the closure plate to sense misplacement of wafers or missing wafers by mapping their location based on motor displacement. Also provided is a closure plate which is readily detachable from the arm, and further, a bezel insert containing the opening to allow the apparatus to accommodate different sized pods by replacing the closure plate and opening bezel insert to correspond to different size pods. In a further aspect of the present invention, the base comprises a closed container having an opening therein. The closure plate is attached to at least one riser extending through the opening. A vacuum assembly is disposed adjacent to the opening and coupled to an ambient environment, such as the operator side or outside, and operable to provide a vacuum around the opening, whereby particles within the closed container are extractable to the ambient environment.